I’m currently using Nimbus Notes (after migrating to it from Evernote a couple of years ago), and am starting to be very unhappy with it. The only export options it provides are PDF and HTML. If I move to Obsidian, would there be a way to import either of those?
If you want to import them into an Obsidian vault, the PDFs at least would need converted to markdown if you want to do anything more than just read them. Obsidian has native support for reading PDFs, but doesn’t OCR or index them so they aren’t searchable form inside obsidian without a community plug-in. I recommend pandoc for converting.
As markdown is a ~superset of HTML, you could try just copying them over, but you’ll have a better editing experience converting them to markdown first. Again, pandoc for that.